You’re thinking of anti-theist.
Antitheism, also spelled anti-theism, is the philosophical position that theism should be opposed.
Atheists can merely not care if there was a god because they don’t see any proof of it.
Atheism, in the broadest sense, is an absence of belief in the existence of deities.
Atheism can also be more anti than that, but isn’t necessarily always that way
I’ll take JSON over XML any day.
It’s probably worth linking https://www.jsonfeed.org/ when asking this question.